Fix/cache empty repolist error handling

[EngCaioFonseca]

Pull Request Change Description

Summary

Fixes four issues in PostgreSQL data-access and startup error handling. The changes are local and introduce no schema, dependency, or callback-graph changes.

Changes

1. Handle empty repository selections

repo-choices initially contains [], but its callbacks still run. Psycopg2 converted the empty sequence into IN (), causing invalid SQL during initial page loads.

• get_uncached() now returns [] immediately.
• retrieve_from_cache() uses IN (NULL) to return zero rows while preserving DataFrame columns.
• Heatmap and repository-overview callbacks now return cleared or no-data states when no repository is selected.
• get_default_repo_with_data() now returns None instead of indexing an empty list.

This is handled at the data and callback boundaries rather than with prevent_initial_call, which would break navigation with selections restored from session storage.

2. Preserve database error causes

AugurManager.run_query() previously caught every exception and discarded its cause.

It now:

• Catches only Exception, allowing KeyboardInterrupt and SystemExit to propagate.
• Logs the full traceback.
• Chains the original error with raise ... from e.

3. Preserve _bots.py startup failures

If AugurManager() failed, _bots.py continued with an uninitialized dbm, masking the original error with NameError.

The original KeyError or SQLAlchemyError is now logged and re-raised.

4. Correct cache bookkeeping

caching_wrapper() recorded every requested repository, including repositories already cached. This created duplicate bookkeeping rows.

Query parameters and uncached repository IDs now use separate variables, and bookkeeping records only repositories fetched by the current operation.

Result

• Empty repository selections no longer cause SQL or callback errors.
• Database failures retain their original cause and traceback.
• Startup failures are no longer masked.
• Cache bookkeeping no longer adds duplicates for already-cached repositories.

Validation

• Pre-commit hooks and Black formatting pass.
• Changed files compile successfully.
• Independent review found no remaining correctness defects.

Generative AI disclosure

Please select one option:

• This contribution was NOT assisted or created by Generative AI tools.
• This contribution was assisted or created by Generative AI tools.

If AI tools were used, please provide details below:
- What tools were used? Claude Opus 5, GPT 5.6 - sol
- How were these tools used? Draft, multiple iterations, review.
- Did you review these outputs before submitting this PR? Yes.